It is known that in conventional installations, the fabric is unwound from a bobbin or other similar supply support, stretched in the longitudinal direction, run through a coating machine having a doctor blade which deposits a layer of the synthetic material in question on one of its sides. The fabric thus coated then passes through a heating oven, at the outlet of which it may be subjected to a calendering operation by passing between two rotating rollers. Then, it is cooled before being finally wound on a support.
One main drawback encountered in conventional methods resides in transverse shrinkage of the fabric, which shrinkage is particularly severe when dealing with a fabric produced with synthetic fibres (polyamide or polyester). These fibres normally leave the spinning mill in a condition in which they are not heat-fixed, so that they undergo an appreciable shrinkage effect when they are subjected to an elevated temperature. Naturally, shrinkage of this type is a considerable detriment to the value of the fabric/synthetic material complex obtained.
In order to remedy this fault, it has been proposed to produce the basic fabric from yarn stabilized by a heat treatment. However, it will be understood that this is a relatively difficult operation, it also being noted that the cost of the fabric produced from yarn of this type is further increased by the fact that the latter has a weight per meter greater than that of untreated yarn, without having the better mechanical characteristics. Furthermore, fabric made from stabilized yarn has a greater coeffeicient of elongation, which is detrimental in many applications. Finally, and above all, whatever the quality of the stabilization treatment, the shrinkage phenomenon is not completely eliminated.
Now, apart from the above-mentioned drawbacks, the shrinkage of coating fabrics opposes the production of complexes in which the basic fabric is constituted by a mixture of synthetic yarn and natural, artificial or synthetic discontinuous fibres. Coated fabrics of this type would have excellent resistance to tearing owing to the presence of continuous yarn, whilst having a more agreeable texture due to the discontinuous fibres in the case of coating on one side and better adhesion of the coating to the fabric with coating on one or two sides. However, a complex of this type cannot be envisaged at the present time, owing to the very substantial shrinkage differences between the two types of textile fibres, even if the synthetics have been previously treated.